1. Field of the Invention
The invention relates to an electrical machine having a housing, having a stator which is arranged in this housing and has stator winding conductors which are arranged in slots on the internal circumference and are cooled indirectly, and having a rotor, the laminated core of the stator being constructed from individual laminated core elements which are separated from one another by spacer webs, and the intermediate spaces between two successive laminated core elements forming radially running cooling slits, and the cooling slits connecting annular air gap spaces on the internal circumference of the laminated stator core to chamber spaces which are located between the external circumference of the laminated stator core and the housing, which chambers comprise cold-gas chambers which can be acted on by cold cooling gas, and hot-gas chambers into which heated cooling gas flows, directed radially outwards from said cooling slits, which hot-gas chambers are connected to coolers, and cooling-gas conveying means and cooling-gas guidance devices being provided at both machine ends, which means and devices supply the cooled gas to the cold-gas chambers as cold gas and suck the heated cooling gas out of the hot-gas chambers again.
A gas-cooled electrical machine having these features is disclosed, for example, in "Brown Boveri Technik" [Brown Boveri Technology], March/1986, pages 133-138, especially FIG. 3 on page 135.
2. Discussion of Background
The principle of so-called indirect cooling is that the losses which are produced in the stator winding bars are to be passed to the cooling medium (hydrogen or air). In this case, the main heat flow takes place from the bar copper via the insulation into the tooth region of the laminated stator core. From the stator teeth, heat is passed to the cooling medium.
The limits of heating are in this case predetermined by the temperature sensitivity of the insulation and, furthermore, by corresponding maximum temperatures which are defined in Standards by different insulation classes (ANSI, IEC).
As a consequence of the relatively large temperature difference between the stator copper embedded in the insulation and the outer layer of insulation, the maximum power of an indirectly gas-cooled turbogenerator using the classic cooling principle is limited.
There has thus been no absence of proposals to improve the cooling, these efforts concentrating mainly on intensifying the cooling in the central machinery region.
Thus, EP-B-0 279 064 describes a gas-cooled electrical machine in which the hot-gas chambers in the central region of the machine are connected via separate lines, bypassing the end warm-gas chambers, directly to the coolers. This prevents the heated cooling gas from the central hot-gas chambers mixing with that from the end hot-gas chambers, and it is possible to split the volume flows through the individual cooling slits and the air gap and chamber spaces allocated to them such that virtually complete leveling of the temperature profile in the machine longitudinal direction results.
This measure has been best proven in the case of new designs. However, it can be carried out only at considerable cost in the case of machines which are already in operation.